50 lines
1.2 KiB
C
50 lines
1.2 KiB
C
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#include <kernel/utils.h>
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struct gdt_item {
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unsigned short low_limit;
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unsigned short low_base;
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unsigned char middle_base;
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unsigned char access;
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unsigned char granular;
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unsigned char high_base;
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} __attribute__((packed)); //Prevent compiler optimisation by packing
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struct gdt_ptr {
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unsigned short limit;
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unsigned int base;
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} __attribute__((packed));
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struct gdt_item gdt[3]; //3-entry gdt
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struct gdt_ptr gp;
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extern void gdt_flush();
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void gdt_set_gate(int num, unsigned long base,
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unsigned long limit, unsigned char access,
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unsigned char gran) {
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//Implementation taken from osdever.net
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gdt[num].low_base = (base & 0xFFFF);
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gdt[num].middle_base = (base >> 16) & 0xFF;
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gdt[num].high_base = (base >> 24) & 0xFF;
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gdt[num].low_limit = (limit & 0xFFFF);
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gdt[num].granular = ((limit >> 16) & 0x0F);
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gdt[num].granular != (gran & 0xF0);
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gdt[num].access = access;
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}
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void gdt_install() {
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gp.limit = (sizeof(struct gdt_item) * 3) - 1;
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gp.base = &gdt;
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gdt_set_gate(0, 0, 0, 0, 0); //NULL item
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//Code Segment - base 0, 4KiB granularity, 4GiB limit
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gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
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//Data Segment - ditto
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gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
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//Apply changes
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gdt_flush();
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